L. Dal Negro

Light emission from silicon-rich nitride nanostructures

Light-emitting Si-rich silicon nitride (SRN) films were fabricated by plasma enhanced chemical vapor deposition followed by low temperature (500–900°C) annealing. The optical properties of SRN films were studied by micro-Raman and photoluminescence spectroscopy and indicate the presence of small Si clusters characterized by broad near-infrared emission, large absorption/emission Stokes shift, and nanosecond recombination. Our results are supported by first-principles simulations indicating that N atoms bonded to the surface of nanometer Si clusters play a crucial role in the emission mechanism of SRN films. Light emission from SRN systems can provide alternative routes towards the fabrication of optically active Si devices.

Light emission efficiency and dynamics in silicon-rich silicon nitride films

Light-emitting Si-rich silicon nitride (SRN) films were fabricated by plasma enhanced chemical vapor deposition followed by thermal annealing and the SRN external quantum efficiency was measured. The SRN light emission temperature dependence and recombination dynamics were also studied. Small emission thermal quenching from 4 to 330 K with wavelength dependent, nanosecond recombination lifetime was observed. Light emission from SRN systems can provide alternative routes towards the fabrication of efficient Si-based optical devices.

Photon band gap properties and omnidirectional reflectance in Si∕SiO2 Thue–Morse quasicrystals

Aperiodic one-dimensional Si∕SiO2 Thue–Morse (T–M) multilayer structures have been fabricated in order to investigate both the band gap properties with respect to the system size (band gap scaling) and the omnidirectional reflectance at the fundamental optical band gap. Variable angle reflectance data have experimentally demonstrated a large reflectance band gap in the optical spectrum of a T–M quasicrystal, in agreement with transfer matrix simulations. We explain the physical origin of the T–M omnidirectional band gap as a result of periodic spatial correlations in the complex T–M structure. The unprecedented degree of structural flexibility of T–M systems can provide an attractive alternative to photonic crystals for the fabrication of photonic devices.

Spectrally enhanced light emission from aperiodic photonic structures

Light-emitting silicon-rich, SiNx∕SiO2 Thue-Morse (T-M) multilayer structures have been fabricated in order to investigate the generation and transmission of light in strongly aperiodic deterministic dielectrics. Photoluminescence and optical transmission data experimentally demonstrate the presence of emission enhancement effects occurring at wavelengths corresponding to multiple T-M resonance states. Emission enhancement effects by a factor of almost 6 with respect to homogeneous SiNx dielectrics have been experimentally measured, in good agreement with transfer matrix simulations. The unprecedented degree of structural flexibility of T-M systems can provide alternative routes towards the fabrication of optically active multiwavelength photonic devices.

Electroluminescence from Er-doped Si-rich silicon nitride light emitting diodes

Electrical devices based on Erbium (Er) doping of silicon nitride have been fabricated by reactive cosputtering and intense, room temperature Er electroluminescence was observed in the visible (527, 550, and 660 nm) and near-infrared (980 and 1535 nm) spectral ranges at low injection voltages (<5 V EL turn on). The electrical transport mechanism in these devices was investigated and the excitation cross section for the 1535 nm Er emission was measured under electrical pumping, resulting in a value (1.2×10−15 cm2) comparable to optical pumping. These results indicate that Er-doped silicon nitride has a large potential for the engineering of light sources compatible with Si technology.

Electroluminescence from silicon-rich nitride/silicon superlattice structures

Luminescent silicon-rich nitride/silicon superlattice structures (SRN/Si-SLs) with different silicon concentrations were fabricated by direct magnetron cosputtering deposition. Rapid thermal annealing at 700 °C resulted in the nucleation of small amorphous Si clusters that emit at 800 nm under both optical and electrical excitations. The electrical transport mechanism and the electroluminescence (EL) of SRN/Si-SLs have been investigated. Devices with low turn-on voltage (6 V) have been demonstrated and the EL mechanism has been attributed to bipolar recombination of electron-hole pairs at Si nanoclusters. Our results demonstrate that amorphous Si clusters in SRN/Si-SLs provide a promising route for the fabrication of Si-compatible optical devices.

Sensitized erbium emission from silicon-rich nitride/silicon superlattice structures

Erbium-doped silicon-rich nitride/silicon superlattice structures were fabricated by direct magnetron cosputtering deposition on Si substrates. Rapid thermal annealing resulted in the nucleation of small amorphous Si clusters, which efficiently sensitize 1.54μm emission via a nanosecond-fast nonresonant energy transfer process, providing an alternative route toward the fabrication of Si-compatible devices based on Er sensitization.

Energy transfer and 1.54 μm emission in amorphous silicon nitride films

Er-doped amorphous silicon nitride films with various Si concentrations (Er:SiNx) were fabricated by reactive magnetron cosputtering followed by thermal annealing. The effects of Si concentrations and annealing temperatures were investigated in relation to Er emission and excitation processes. Efficient excitation of Er ions was demonstrated within a broad energy spectrum and attributed to disorder-induced localized transitions in amorphous Er:SiNx. A systematic optimization of the 1.54 μm emission was performed and a fundamental trade-off was discovered between Er excitation and emission efficiency due to excess Si incorporation. These results provide an alternative approach for the engineering of sensitized Si-based light sources and lasers.

Temperature dependence of the energy transfer from amorphous silicon nitride to Er ions

The 1.54 μm photoluminescence and decay time of Er-doped amorphous silicon nitride films with different Si concentrations are studied in the temperature range of 4 to 320 K. The temperature quenching of the Er emission lifetime demonstrates the presence of nonradiative trap centers due to excess Si in the films. The temperature dependence and the dynamics of the energy coupling between amorphous silicon nitride and Er ions are investigated at different temperatures using two independent methods, which demonstrate phonon-mediated energy coupling. These results can lead to the engineering of more efficient Er-doped, Si-based light sources for on-chip nanophotonics applications.

Carrier dynamics and erbium sensitization in silicon-rich nitride nanocrystals

Ultrafast two-color pump-probe measurements, time-resolved photoluminescence (TRPL), and photoluminescence excitation measurements were performed on Si-rich nitride (SRN) and Er doped SRN (Er:SRN) nanocrystals samples. Transient absorption data were compared with picosecond TRPL and excited state absorption cross (ESA) sections σ were measured at different wavelengths. Our data show that σ in Er:SRN, which is approximately 10−19cm2 at 1.54μm, does not scale with the ∼λ2 behavior predicted by simple free carrier absorption models. Finally, our data demonstrate that in Er:SRN efficient energy transfer to Er ions occurs on the nanosecond time scale with reduced ESA compared to Er-doped oxide-based systems.